The present invention is directed to a method and apparatus for the manufacture of an optical transmission element comprising at least one light waveguide lead which is passed through two coating stations for the application of a filling compound in two layers and which is then, subsequently provided with an envelope.
A method for applying two coatings onto a transmission element, which has at least one or more optical waveguides, is disclosed in U.S. Pat. No. 4,474,638, which claims priority from German Application No. 32 07 083, and whose disclosure is incorporated by reference thereto. In the device of the patent, a light waveguide bundle is passed through a first moistening means, which is provided with a filling compound and has a discharge tube through which the bundle of leads with the filling compound is discharged. This filling tube extends through a second filling device, which has a concentric discharge tube so that a layer of the second filling material, which is under pressure, moves between the concentrically arranged first and second discharge tubes. These discharge tubes terminate within an extruder head in the region of the stretched cone of the envelope which is being applied so that the bundle with the first and second layers of filling compounds are introduced inside of the cone as the outer envelope is being extruded thereon.
Given transmission elements comprising light waveguides which are embedded in a soft filling compounds, care must be exercised to see that the material does not have any air inclusions or at least have very small air inclusions in terms of the volume of the material present. Otherwise, there is a risk that at a great temperature elevation, damage to the sensitive light waveguides can occur in the framework of the expansion of the air bubbles in the filling compound.